/* inffast.c -- fast decoding
 * Copyright (C) 1995-2008, 2010, 2013 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "zutil.h"
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"

#ifndef ASMINF

/* Allow machine dependent optimization for post-increment or pre-increment.
   Based on testing to date,
   Pre-increment preferred for:
   - PowerPC G3 (Adler)
   - MIPS R5000 (Randers-Pehrson)
   Post-increment preferred for:
   - none
   No measurable difference:
   - Pentium III (Anderson)
   - M68060 (Nikl)
   */
#ifdef POSTINC
#  define OFF 0
#  define PUP(a) *(a)++
#else
#  define OFF 1
#  define PUP(a) *++(a)
#endif

/*
   Decode literal, length, and distance codes and write out the resulting
   literal and match bytes until either not enough input or output is
   available, an end-of-block is encountered, or a data error is encountered.
   When large enough input and output buffers are supplied to inflate(), for
   example, a 16K input buffer and a 64K output buffer, more than 95% of the
   inflate execution time is spent in this routine.

   Entry assumptions:

   state->mode == LEN
   strm->avail_in >= 6
   strm->avail_out >= 258
   start >= strm->avail_out
   state->bits < 8

   On return, state->mode is one of:

   LEN -- ran out of enough output space or enough available input
   TYPE -- reached end of block code, inflate() to interpret next block
   BAD -- error in block data

Notes:

- The maximum input bits used by a length/distance pair is 15 bits for the
length code, 5 bits for the length extra, 15 bits for the distance code,
and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
Therefore if strm->avail_in >= 6, then there is enough input to avoid
checking for available input while decoding.

- The maximum bytes that a single length/distance pair can output is 258
bytes, which is the maximum length that can be coded.  inflate_fast()
requires strm->avail_out >= 258 for each loop to avoid checking for
output space.
*/
void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start)
{
   struct inflate_state FAR *state;
   unsigned char FAR *in;      /* local strm->next_in */
   unsigned char FAR *last;    /* have enough input while in < last */
   unsigned char FAR *out;     /* local strm->next_out */
   unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
   unsigned char FAR *end;     /* while out < end, enough space available */
#ifdef INFLATE_STRICT
   unsigned dmax;              /* maximum distance from zlib header */
#endif
   unsigned wsize;             /* window size or zero if not using window */
   unsigned whave;             /* valid bytes in the window */
   unsigned wnext;             /* window write index */
   unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
   unsigned long hold;         /* local strm->hold */
   unsigned bits;              /* local strm->bits */
   code const FAR *lcode;      /* local strm->lencode */
   code const FAR *dcode;      /* local strm->distcode */
   unsigned lmask;             /* mask for first level of length codes */
   unsigned dmask;             /* mask for first level of distance codes */
   code here;                  /* retrieved table entry */
   unsigned op;                /* code bits, operation, extra bits, or */
   /*  window position, window bytes to copy */
   unsigned len;               /* match length, unused bytes */
   unsigned dist;              /* match distance */
   unsigned char FAR *from;    /* where to copy match from */

   /* copy state to local variables */
   state = (struct inflate_state FAR *)strm->state;
   in = strm->next_in - OFF;
   last = in + (strm->avail_in - 5);
   out = strm->next_out - OFF;
   beg = out - (start - strm->avail_out);
   end = out + (strm->avail_out - 257);
#ifdef INFLATE_STRICT
   dmax = state->dmax;
#endif
   wsize = state->wsize;
   whave = state->whave;
   wnext = state->wnext;
   window = state->window;
   hold = state->hold;
   bits = state->bits;
   lcode = state->lencode;
   dcode = state->distcode;
   lmask = (1U << state->lenbits) - 1;
   dmask = (1U << state->distbits) - 1;

   /* decode literals and length/distances until end-of-block or not enough
      input data or output space */
   do {
      if (bits < 15) {
         hold += (unsigned long)(PUP(in)) << bits;
         bits += 8;
         hold += (unsigned long)(PUP(in)) << bits;
         bits += 8;
      }
      here = lcode[hold & lmask];
dolen:
      op = (unsigned)(here.bits);
      hold >>= op;
      bits -= op;
      op = (unsigned)(here.op);
      if (op == 0) {                          /* literal */
         Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
                  "inflate:         literal '%c'\n" :
                  "inflate:         literal 0x%02x\n", here.val));
         PUP(out) = (unsigned char)(here.val);
      }
      else if (op & 16) {                     /* length base */
         len = (unsigned)(here.val);
         op &= 15;                           /* number of extra bits */
         if (op) {
            if (bits < op) {
               hold += (unsigned long)(PUP(in)) << bits;
               bits += 8;
            }
            len += (unsigned)hold & ((1U << op) - 1);
            hold >>= op;
            bits -= op;
         }
         Tracevv((stderr, "inflate:         length %u\n", len));
         if (bits < 15) {
            hold += (unsigned long)(PUP(in)) << bits;
            bits += 8;
            hold += (unsigned long)(PUP(in)) << bits;
            bits += 8;
         }
         here = dcode[hold & dmask];
dodist:
         op = (unsigned)(here.bits);
         hold >>= op;
         bits -= op;
         op = (unsigned)(here.op);
         if (op & 16) {                      /* distance base */
            dist = (unsigned)(here.val);
            op &= 15;                       /* number of extra bits */
            if (bits < op) {
               hold += (unsigned long)(PUP(in)) << bits;
               bits += 8;
               if (bits < op) {
                  hold += (unsigned long)(PUP(in)) << bits;
                  bits += 8;
               }
            }
            dist += (unsigned)hold & ((1U << op) - 1);
#ifdef INFLATE_STRICT
            if (dist > dmax) {
               strm->msg = (char *)"invalid distance too far back";
               state->mode = BAD;
               break;
            }
#endif
            hold >>= op;
            bits -= op;
            Tracevv((stderr, "inflate:         distance %u\n", dist));
            op = (unsigned)(out - beg);     /* max distance in output */
            if (dist > op) {                /* see if copy from window */
               op = dist - op;             /* distance back in window */
               if (op > whave) {
                  if (state->sane) {
                     strm->msg =
                        (char *)"invalid distance too far back";
                     state->mode = BAD;
                     break;
                  }
#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
                  if (len <= op - whave) {
                     do {
                        PUP(out) = 0;
                     } while (--len);
                     continue;
                  }
                  len -= op - whave;
                  do {
                     PUP(out) = 0;
                  } while (--op > whave);
                  if (op == 0) {
                     from = out - dist;
                     do {
                        PUP(out) = PUP(from);
                     } while (--len);
                     continue;
                  }
#endif
               }
               from = window - OFF;
               if (wnext == 0) {           /* very common case */
                  from += wsize - op;
                  if (op < len) {         /* some from window */
                     len -= op;
                     do {
                        PUP(out) = PUP(from);
                     } while (--op);
                     from = out - dist;  /* rest from output */
                  }
               }
               else if (wnext < op) {      /* wrap around window */
                  from += wsize + wnext - op;
                  op -= wnext;
                  if (op < len) {         /* some from end of window */
                     len -= op;
                     do {
                        PUP(out) = PUP(from);
                     } while (--op);
                     from = window - OFF;
                     if (wnext < len) {  /* some from start of window */
                        op = wnext;
                        len -= op;
                        do {
                           PUP(out) = PUP(from);
                        } while (--op);
                        from = out - dist;      /* rest from output */
                     }
                  }
               }
               else {                      /* contiguous in window */
                  from += wnext - op;
                  if (op < len) {         /* some from window */
                     len -= op;
                     do {
                        PUP(out) = PUP(from);
                     } while (--op);
                     from = out - dist;  /* rest from output */
                  }
               }
               while (len > 2) {
                  PUP(out) = PUP(from);
                  PUP(out) = PUP(from);
                  PUP(out) = PUP(from);
                  len -= 3;
               }
               if (len) {
                  PUP(out) = PUP(from);
                  if (len > 1)
                     PUP(out) = PUP(from);
               }
            }
            else {
               from = out - dist;          /* copy direct from output */
               do {                        /* minimum length is three */
                  PUP(out) = PUP(from);
                  PUP(out) = PUP(from);
                  PUP(out) = PUP(from);
                  len -= 3;
               } while (len > 2);
               if (len) {
                  PUP(out) = PUP(from);
                  if (len > 1)
                     PUP(out) = PUP(from);
               }
            }
         }
         else if ((op & 64) == 0) {          /* 2nd level distance code */
            here = dcode[here.val + (hold & ((1U << op) - 1))];
            goto dodist;
         }
         else {
            strm->msg = (char *)"invalid distance code";
            state->mode = BAD;
            break;
         }
      }
      else if ((op & 64) == 0) {              /* 2nd level length code */
         here = lcode[here.val + (hold & ((1U << op) - 1))];
         goto dolen;
      }
      else if (op & 32) {                     /* end-of-block */
         Tracevv((stderr, "inflate:         end of block\n"));
         state->mode = TYPE;
         break;
      }
      else {
         strm->msg = (char *)"invalid literal/length code";
         state->mode = BAD;
         break;
      }
   } while (in < last && out < end);

   /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
   len = bits >> 3;
   in -= len;
   bits -= len << 3;
   hold &= (1U << bits) - 1;

   /* update state and return */
   strm->next_in = in + OFF;
   strm->next_out = out + OFF;
   strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
   strm->avail_out = (unsigned)(out < end ?
         257 + (end - out) : 257 - (out - end));
   state->hold = hold;
   state->bits = bits;
   return;
}

/*
   inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
   - Using bit fields for code structure
   - Different op definition to avoid & for extra bits (do & for table bits)
   - Three separate decoding do-loops for direct, window, and wnext == 0
   - Special case for distance > 1 copies to do overlapped load and store copy
   - Explicit branch predictions (based on measured branch probabilities)
   - Deferring match copy and interspersed it with decoding subsequent codes
   - Swapping literal/length else
   - Swapping window/direct else
   - Larger unrolled copy loops (three is about right)
   - Moving len -= 3 statement into middle of loop
   */

#endif /* !ASMINF */
